Electronic waveguide switch



June 4, 1963 H. c. HANKS, JR

ELECTRONIC WAVEGUIDE SWITCH Filed March 14, 1958 HUGH c HAN INVENTOR JR. ATTORNE; I

3,092,788 ELECTRONIC WAVEGUIDE SWITCH Hugh C. Hanks, Jn, Towson, Md., asslgnor to Martin- Marietta Corporation, a corporation of Maryland Filed Mar. 14, 1958, Ser. No. 721,556 3 Claims. ((11. 333-11) The present invention relates to apparatus for selectively switching electromagnetic energy within an electrical waveguide system, and more particularly to such apparatus wherein the switching is efiected electronically as distinguished from mechanical methods.

The invention has for its principal object the control of the propagation of electromagnetic energy in a waveguide system such that the energy may be selectively directed to one or more of a plurality of output terminals and selectively divided therebetween. Heretofore control switching has been accomplished mechanically. This type of control suifers from the following disadvantages: (a) a long switching cycle, (1)) frequent and large mismatches during a switching cycle, and (c) a physically large size.

The present invention provides apparatus for electronic rather than mechanical switching of electromagnetic energy within a waveguide system. This apparatus has none of the above-listed disadvantages and further permits a large latitude in design configuration.

It is well known that in order for electromagnetic energy to be coupled from one waveguide section into an-' other the latter waveguide section must have a dimension in its H plane which is at least one-half of the wave length of the propagated electromagnetic energy, and, in addition, the electromagnetic energy entering the latter Waveguide section must be properly oriented. Such cou pling has successfully been effected in the past by the use of ferrite elements. it has now been found that ferrite elements also provide means for electronically switching electromagnetic energy within a waveguide system.

According to the invention waveguide switching is eflected by first providing a waveguide system having a common input waveguide section for the propagation of the electromagnetic energy. An impedance element is electrically associated with this input waveguide section to urge the electromagnetic energy therethrough in a given direction. A plurality of output waveguide sections may then be separately connected into the input waveguide section. Each output waveguide section is provided with means adapted to couple the electromagnetic energy from the common waveguide section thereinto. The electronic switching may then be effected by mounting a separate ferrite element in each of the output waveguide sections. Further, means are provided for selectively applying a separate magnetic field parallel to the axis of each of the output waveguide sections and to the ferrite element therewithin.

The selective application of magnetic fields to the ferrite element within the waveguide system of the invention provides electronic waveguide switching which may be rapidly controlled both as to the selection of the output waveguide sections into which electromagnetic energy is to be coupled, and as to the division in magnitude of the electromagnetic energy between the selected output waveguide sections and the common input section. This is explained by noting the effect a magnetic field has on the coupling by a ferrite element of electromagnetic energy from one waveguide section into another wave guide section. For example, assume the waveguide sections are oriented such that the ferrite element provides a high degree of coupling. With the establishment of a magnetic field about the ferrite element, the E vector, that is, the electric field, of the coupled electromagnetic energy propagated may be caused to rotate, the amount of rotation being proportional to the magnitude of the applied magnetic field. This rotation of the E vector causes a portion of the coupled electromagnetic energy to be reflected back, the amount of energy thus reflected being proportional to the degree of E vector rotation. In this way, a selected proportion of electromagnetic energy may be coupled at will, the remainder being reflected back. The limiting condition exists when the magnitude of the magnetic field is su-fdcient to cause the E vector to rotate exactly at which time the total amount of energy is reflected back into the input waveguide section and no coupling at all takes place. It can thus be seen that in a system as provided by the invention selective switching can be effected by conventional electronic means designed for switching and controlling the magnitude of the separate magnetic fields applied to the ferrite coupling elements.

In the above description the application of the magnetic fields limits or prevents the coupling of electromagnetic energy. However, the waveguide system of the invention may be designed so that the opposite is true. In such arrangement the waveguide sections are physically rotated through an angle or" 90 relative to one another so that no energy is ordinarily coupled from one to the other. The E vector rotation caused by the magnetic fields then effects a coupling of electromagnetic energy rather than a reflection as hereinbefore. Again the limiting condition, in this case the total coupling of energy, will take place when the magnetic field is of such intensity as to rotate the E vector through an angle of 90.

Due to the nature of the present invention extremely rapid waveguide switching may be effected by means of conventional electronic equipment designed to selectively apply a separate magnetic field to each of the ferrite elements in the waveguide system. For this reason the present invention may be advantageously employed for switching between a plurality of antennas and either a transmitter or receiver circuit. For example, by means of the invention the transmitter or receiver circuits may be rapidly switched fromone antenna to another. Further, the invention may be employed to selectively divide electromagnetic energy among the plurality of antennas. Also, rapid scanning of the antennas may be obtained by the provision of appropriate sequential switching means. Other advantages of the invention deriving from its electronic nature are no moving parts and a theoretically unlimited number of output sections.

The invention can best be understood by referring to the following drawings in which:

FIG. 1 is a plan view of multiplex switching apparatus in accordance with the invention;

FIG. 2 is a section taken along line 22 of FIG. 1;

FIG. 3 is an alternative embodiment of waveguide switching apparatus in accordance with the invention shown in plan view;

FIG. 4 is a section taken along line 44 of FIG. 3.

Referring first to the embodiment of FIGS. 1 and 2, electromagnetic energy from a waveguide system is connected into a common waveguide section 1. The waveguide may be of any conventional shape such as circular, ridged, or, as shown, rectangular. An impedance element is electrically associated with the common wave guide section to urge the electromagnetic energy therethrough in a given direction as shown by the arrows. The impedance element is illustrated schematically in FIG. 1 as resistor 2.

Normally the electromagnetic energy would propagate undisturbed through the common waveguide section in accordance with Maxwells equations. It is the object of the present invention, however, to provide apparatus which is capable of selectively switching energy from the common waveguide section into any one or more of a plurality of output waveguide sections. To this end the desired plurality of output waveguide sections N (in this case N=3) are separately connected into the common waveguide section. These output sections are identified by the letters A, B, and C.

Each of these output waveguide sections comprises a conventional waveguide 3 and an intermediate waveguide, shown generally at 4. The intermediate waveguides are connected to the waveguide Sby means of bolted flanges and to the common waveguide section 1 by solder. The intermediate waveguides also include ferrite element 5 which extends into the common waveguide section 1 through the intermediate waveguide 4, into the waveguide 3. Advantageously a Teflon bushing 6 may be provided in order to insulate the ferrite element 5 from the metallic portions through which it passes. In the embodiment of FIG. 1 the ferrite element is made rod shaped of circular cross-section and is mounted in axial alignment with waveguide section 3. Further, the ferrite element passes coaxially through a circular hollow cylinder 7 filled with the Teflon insulating bushing thus forming, in efiect, a circular waveguide section.

Each ferrite coupling arrangement according to the invention performs two functions, coupling and gating. First, it couples electromagnetic energy from the common waveguide section into the output waveguide section of which it forms a part. This results from the protrusion of the ferrite element 5 into the common waveguide section. The ferromagnetic properties of the ferrite elements effect a perturbation of the electric and magnetic fields of configuration within the common waveguide section. The coupling then is a combination of both electric and magnetic phenomena and is a function of (l) the depth of insertion of the ferrite element into the common waveguide section, and (2) the diameter of the ferrite element.

Ordinarily the electromagnetic energy would thus be diverted from its course down the common waveguide section into' the output waveguide sections by the coupling effected in the ferrite elements 5. However, the second function of the intermediate waveguide 4 is to control this ferrite coupling phenomenon. Such control is accomplished by gating means which either permit the coupled electromagnetic energy to propagate along the output waveguide section or prevent it from so doing.

This gating is efiected by means for selectively applying a separate magnetic field to each of the ferrite elements. Advantageously such means comprises a separate electromagnet 8 for each output waveguide section. 0

Each of these magnets is so arranged and adapted as to apply a predetermined magnetic field parallel to the axis of its output waveguide section and to the ferrite element therewithin. In this particular embodiment the electromagnet is arranged about the circular waveguide section 7 in coaxial relationship therewith so as to apply a magnetic field parallel to the axis of the ferrite element 5. The gating is then effected by the phenomenon of Faraday rotation which results from the application of a magnetic field to a ferrite element in the direction of the propagation of electromagnetic energy therethrough. In order for Faraday rotation to take place, however, the output waveguide sections must be limited to a rectangular cross-section configuration. A wide variety within such limitation is permissible, however, such as, for example, ridged rectangular and the 4 fields. Thus if the direction of either field is reversed, the direction of travelis also reversed.

The application of an external magnetic field parallel to the axis of a ferrite element causes the propagated electric field coupled through the ferrite element to rotate. The amount of this rotation is proportional to the magnitude of the magnetic field applied. In this way, the electric field may be made to rotate through an angle of exactly 90 by the application of a magnetic field of the proper magnitude. A 90 rotation is the limiting condition at which 'no coupling through the ferrite element into the rectangular output waveguide section associated therewith can take place. Rather, with an angle of rotation of 90 the electromagnetic energy propagating through the ferrite element is caused to reverse its direction and return back through the ferrite element. In returning through the ferrite element the electric field undergoes another 90 rotation thereby undergoing a complete rotation through 180 enabling the electromagnetic energy to be coupled back into the input waveguide section. In this way the intermediate waveguide 4 may be designed so as to effectively set up a gate blocking passage of electromagnetic energy into the output waveguide section. The design considerations determining the angle of rotation of the propagated electric field are the length of the ferrite element and the magnitude of the applied magnetic field; therefore, the shorter the ferrite element the greater the field required.

It will thus be seen that, with this arrangement according to the invention, the accomplishment of the desired switching within the waveguide system is a matter of selectively applying magnetic fields of proper magnitude to the ferrite elements 5. This selective application may be advantageously effected by providing the separate electromagnet 8 for each ferrite element with a separate connection through an on-off switch 9 to a power supply 10. In this way one or more of the electromagnets may be energized thereby to selectively control the switching of electromagnetic energy from the common waveguide section into the output waveguide sections.

The waveguide switching operation is therefore accomplished in the following manner. As energy propagates down the common waveguide section it is interrupted in its course by the coupling influence of the first ferrite element 5 associated with output waveguide section A. This coupling tends to urge the electromagnetic energy from the common waveguide section into waveguide section A. With the switch 9 open no gate is set up to prevent the energy from traveling down the ferrite filled circular waveguide 4 into the waveguide 3. Thus, the electromagnetic energy is switched into output waveguide section A when switch 9 is in its open position.

The insertion loss resulting from this switching operation is dependent upon the following three functions: (1) the coupling efiiciency from the common waveguide section to the ferrite element, (2) the loss caused within the ferrite element, and (3) the coupling efiiciency from the ferrite element into the output waveguide section. The first function is controlled by the diameter of the ferrite element and the depth of insertion of the ferrite element into the waveguide. The loss within the ferrite element is primarily -a function of the type of ferrite and can be minimized by keeping the length of the ferrite element as short as possible.

Assume, however, that it is desired to propagate the electromagnetic energy through common waveguide section 1 without being coupled into the output waveguide section A. It then becomes necessary to prevent the'passage of energy into section A by closing the gate within the intermediate waveguide 4. This is efiected by closing the switch 9 to apply the magnetic field from electromagnet 8 to the the ferrite element 5. The energy tending to travel down the ferrite filled waveguide is thus reflected back into the common waveguide section 1.

Without any preliminary design adaptation in, the

common waveguide section 1 the electromagnetic energy from section A might travel in either direction upon being reflected back into the common waveguide section. The division which would thus result may be prevented, however, by designing the common waveguide section such that the impedance seen by the reflected electromagnetic energy is lower in the desired direction of travel. Such design has been shown schematically in FIG. 1 by the impedance symbol 2.

The switching procedure above described is, of course, also applicable to the other output waveguide sections B and C. It should be noted at this point that this switching can be made reciprocal with respect to the inputs and outputs. That is, energy may be applied through any one of the waveguide sections A, B, or C into the common waveguide section and then coupled selectively into the remaining output waveguide sections. Thus the electromagnetic energy within the common waveguide section may be switched from one output to another to effect the switching of electromagnetic energy by electronic rather than mechanical methods.

In addition to the advantages of selective electronic waveguide switching hereinbefore described, the invention further provides the means for effecting a division, in magnitude, of the electromagnetic energy propagated through the common waveguide section 1 among one or more of the output waveguide sections. This additional feature results from the determination that the degree of rotation of the electric field propagating through the ferrite element is proportional to the magnitude of the external magnetic field applied thereto. Further, the percentage of the total electromagnetic energy reflected back into the input waveguide section varies in proportion to the degree of rotation of the electric field. Thus, by the provision of means for selectively controlling the magnitude of the magnetic field applied to the separate ferrite elements, division of the magnetic field within well-defined limits may be effected.

For example, 50 percent of the energy of the input waveguide section may be coupled into output waveguide section A by controlling the intensity of the magnetic field applied to fern'teelement 5 so as to eifect a 45 rotation of the E vector. In this wa only 50 percent of the electromagnetic energy will be returned back to the input waveguide section thereby effecting the desired division. Thus, by controlling the magnitude of the magnetic field so as to cause rotation of the E vector between zero and 90, any level of energy transfer between 0 percent and *1 00 percent can theoretically be achieved. Control of the magnitudes of the separate magnetic fields may be efiected by the provision of conventional electronic potentiometer control elements 20 connected to the output of the power supply and separately connected in each one of the electromagnet lines.

A waveguide switch similar to that of FIGS. 1 and 2 was built and tested over the frequency range of 9.l-l0 kmc. The intermediate waveguide section was designed to operate above 8.8 kmc. Tests were run to determine the insertion loss and impedance as a function of (l) the insertion distance of the ferrite element into the common waveguide section and (2) the impedance 2 in the form of a termination for the common waveguide section. A series of terminations were used including (1) matched load, (2) a short circuit, (3) an open circuit, and (4) an optimum load. These tests verified the recited advantages of the multiplex switch of this invention.

Further advantages of the invention derive from the electronic nature of the waveguide switching thereby eiiected. The electronic switching results in the elimination of moving parts, the ability to have as many output waveguide sections as is desired, the ability to divide the electromagnetic energy in magnitude, and further, the provision of extremely rapid switching speeds. The latter two advantages make the waveguide switching system of the invention particularly advantageous for the switching of several antennas to either transmitter or receiver devices. In such application any one or more of the antennas may be selectively switched to the receiver or transmitter. Further, the antennas may be rapidly scanned by the provision of sequential means for switches 9 for the selective application of the separate electromagnetic fields. Or, if desired, a division of the electromag netic energy between the antennas may be provided by the control devices 20.

It should be noted that the present invention may be operated with the output waveguide sections 3 oriented with respect to the input waveguide section 1 such as to block or partially block the passage of electromagnetic energy therebetween. For example, if the output waveguide sections were physically rotated through an angle of from that position illustrated in FIGS. 1 and 2, they would be so oriented as to make impossible the coupling of electromagnetic energy from one waveguide section into another. In that event the closing of switches 9 would effect an opposite reaction than that described hereinbefore. That is, the application of a magnetic field would effect a rotation of the electric field vector of the propagated electromagnetic energy so as to permit coupling into the output waveguide section rather than to prevent it as in the embodiment of FIG. 1. Of course, any arrangement of the output waveguide sections intermediate to a complete 90 rotation relative to the arrangement of FIG. 1 is also included within the scope of the invention.

It should also be noted that gating within the output waveguide sections of FIGS. 1 and 2 may also be effected by a phenomenon alternative to Faraday rotation and denoted as waveguide cutoff. This phenomenon also results from the application of a magnetic field to the ferrite elements 5. However, in order for the phenomenon of waveguide cutofl? to occur, the magnetic field applied to the ferrite elements must be substantially greater than that which is applied to efiect Faraday rotation. This is due to the fact that to produce a waveguide beyond cutotf condition enough energy is required to disturb the electric and magnetic configuration Within the waveguide to such an extent that the waveguide is no longer capable of supporting the propagation of energy. Correspondingly, however, a 60 db reduction of energy may be obtained by the use of a waveguide beyond cutoff condition compared to the 30 db reduction of energy produced by Faraday rotation. Further, the use of the waveguide cutofi phenomenon permits the output waveguide sections to employ configurations other than rectangular as is required in the case of Faraday rotation.

FIGS. 3 and 4 illustrate an alternative embodiment of the invention which permits greater control over the division of energy in the common waveguide section as described above. The apparatus again comprises a common waveguide section 1 and output waveguide sections A, B, and C. This embodiment difiers primarily in the provisions for coupling electromagnetic energy from the common waveguide section 1 into the output waveguide sections. As shown by the figure no intermediate waveguide is employed to effect the coupling as was done in the embodiment of FIG. '1. Rather, the output Waveguide sections are connected directly to the common waveguide section 1. Coupling is eifected by means of ferrite elements 11, preferably slab shaped, mounted within the common waveguide section and separated therefrom by Teflon insulation 12'. Each of these ferrite elements 11 is individually associated with a separate output waveguide section and is mounted beside the waveguide section associated therewith. A separate coupling electromagnet 12 is provided for each of these coupling ferrite elements 11. The electromagnets are so positioned as to apply a predetermined magnetic field parallel to the axis of the common waveguide section and to the ferrite elements associated therewith. Each electromagnetic and ferrite element combination forms a coupling unit. These are labeled A, B, and C, respectively, to designate their association with the correspondingly labeled output waveguide sections.

Coupling into an output waveguide section by means of these coupling units is accomplished in the following manner. As energy propagates down the common waveguide section it approaches the coupling ferrite element 11 of unit A. If the electromagnet 12 associated therewith is unenergized the electromagnetic energy will pass on beyond this point. Energization of the electromagnet, however, causes the electric and magnetic field configuration within the common waveguide section to change such that propagation is no longer permitted in the for- .ard direction at that point. By proper placement of the ferrite element 11 as described above, the electromagnetic energy may be turned into the output waveguide section A to efiect the desired coupling. This same coupling procedure is also applicable for the units 13' and C associated with the output waveguide sections B and C, respectively. To enable selective coupling through this medium each electromagnet 12 is separately connected to a switch 13 to a power supply 14.

Further control of the waveguide switching is provided by the positioning of separate gating ferrite elements 15 in each of the output waveguide sections. These ferrite elements are mounted within the output waveguide section by Teflon insulation 16. A separate gating electromagnet 17 is provided for each of the gating ferrite elements and is mounted and arranged so as to apply a magnetic field parallel to the axis of the output waveguide section and to the ferrite element associated therewith. Separate switching means 18 are also provided so that each electromagnet may be selectively switched into operation.

The gating ferrite elements 15 have the same effect as do the coupling fer-rite elements 11 in that when energized they render the output waveguide sections unilateral as far as the propagation of electromagnetic energy therethrough is concerned. Thus, energy coupled thereinto by means of the coupling units may be rejected or passed on depending upon the position of the switch 18. In operation then the apparatus of FIGS. 3 and 4 may be operated to effect selective multiplex switching by the use of switches 13 and 18. Further, the unit is reciprocal in nature in that energy may be applied through any one of the output waveguide sections rather than the common waveguide section. In that event, the energy introduced through the output waveguide section may be urged in either direction in the common waveguide section by the selective energization of the coupling units through switches 13. The coupling units therefore effectively function as the impedance 2 of FIG. 1.

Preferred embodiments of the invention have been described. Various changes and modifications may be made in the scope of the invention as set forth in the appended claims.

8 I claim: 1. Apparatus for selectively switching electromagnetic energy'within a waveguide system, comprising a common input Waveguide section for supporting propagation of electromagnetic energy therethrough, aplurality of out guide section, and means for selectively applying a V magnetic field parallel to the axis of each said circular waveguide, section and to the said ferrite element therewithin, said magnetic field having a magnitude sufiicient for causing Faraday rotation of the electromagnetic energy coupled by the said ferrite element associated therewith, thereby to selectively control the switching and power division of electromagnetic energy from said common waveguide section into said output waveguide sections, the amount of electromagnetic energy coupled from said common waveguide section to said output waveguide sectionsbeing a function of the intensity of the parallel magnetic field applied to said ferrite element.

2. Apparatus in accordance with claim 1 in which eachof said. output waveguide sections is orientated with respect to said input waveguide section for presenting waveguide cut-off to the electromagnetic energy propagated in said input waveguide section until said magnetic field is applied to the said ferrite element associated therewith.

3. Apparatus in accordance with claim 1 in which each of said output waveguide sections is oriented with respect 'to' said input waveguide section for coupling 2,686,900 Rigrod Aug. 17,

2,719,274 Luhrs Sept. 27, 1955 2,745,069 Hewitt May 8, 1956 2,798,205 Hogan July 2, 1957 2,870,418 Hewitt Jan. 20, 1959 2,908,872 Garoff Oct. 13, 1959 r 2,961,658 Spencer Nov. 22, 1960 OTHER REFERENCES Theory and Application of Ferrites, Soohoo, Prentice- HallElectrical Engineering Series, 1960, pages 9, 119 and 12.0 of interest. TK7870/ S 55. 

1. APPARATUS FOR SELECTIVELY SWITCHING ELECTROMAGNETIC ENERGY WITHIN A WAVEGUIDE SYSTEM, COMPRISING A COMMON INPUT WAVEGUIDE SECTION FOR SUPPORTING PROPAGATION OF ELECTROMAGNETIC ENERGY THERETHROUGH, A PLURALITY OF OUTPUT WAVEGUIDE SECTIONS EACH HAVING A SUBSTANTIALLY RECTANGULAR CROSS-SECTION, A PLURALITY OF CIRCULAR WAVEGUIDE SECTIONS EACH MOUNTED FOR ELECTROMAGNETIC COUPLING A RESPECTIVE ONE OF SAID OUTPUT WAVEGUIDE SECTIONS TO SAID COMMON INPUT WAVEGUIDE SECTION, A PLURALITY OF ROD-SHAPED FERRITE ELEMENTS, EACH OF SAID FERRITE ELEMENTS HAVING A CIRCULAR CROSS-SECTION AND BEING COAXIALLY MOUNTED IN A RESPECTIVE ONE OF SAID CIRCULAR WAVEGUIDE SECTIONS, EACH SAID FERRITE ELEMENT PROJECTING INTO SAID COMMON WAVEGUIDE SECTION TO PROVIDE COUPLING ELECTROMAGNETIC ENERGY THEREFROM INTO THE ASSOCIATED SAID CIRCULAR WAVEGUIDE SECTION, AND MEANS FOR SELECTIVELY APPLYING A MAGNETIC FIELD PARALLEL TO THE AXIS OF EACH SAID CIRCULAR WAVEGUIDE SECTION AND TO THE SAID FERRITE ELEMENT THEREWITHIN, SAID MAGNETIC FIELD HAVING A MAGNITUDE SUFFICIENT FOR CAUSING FARADAY ROTATION OF THE ELECTROMAGNETIC ENERGY COUPLED BY THE SAID FERRITE ELEMENT ASSOCIATED THEREWITH, THEREBY TO SELECTIVELY CONTROL THE SWITCHING AND POWER DIVISION OF ELECTROMAGNETIC ENERGY FROM SAID COMMON WAVEGUIDE SECTION INTO SAID OUTPUT WAVEGUIDE SECTIONS, THE AMOUNT OF ELECTROMAGNETIC ENERGY COUPLED FROM SAID COMMON WAVEGUIDE SECTION TO SAID OUTPUT WAVEGUIDE SECTIONS BEING A FUNCTION OF THE INTENSITY OF THE PARALLEL MAGNETIC FIELD APPLIED TO SAID FERRITE ELEMENT. 